Inappropriate fertilization and poor management practices in citrus orchards can cause soil acidification, which may result in potential proton (H+) toxicity to citrus roots. It has been reported that boron (B) can mediate H+ detoxification in citrus; however, the mechanisms remain limited. Herein, a hydroponic experiment was employed to unravel the alleviation mechanism of B on H+ toxicity at pH 4 in trifoliate (Poncirus trifoliate (L.) Raf.) seedlings. H+ toxicity reduced cytoplasmic pH from 7.2 (control) to 6.9 and vacuolar pH from 5.6 (control) to 5.4. This severely damaged the plasma membrane (PM) and inhibited root activity by 35%. However, B supplementation restored cytoplasmic pH to 7.1 and vacuolar pH to 5.6, enhancing root activity by 52% and reducing membrane permeability (relative conductivity decreased by 28%). Mechanistically, B upregulated phosphorylated-type adenosine triphosphatase activity by 14%; conversely, it suppressed vacuolar-type adenosine triphosphatase hyperactivity by 9% to stabilize vacuolar pH. Furthermore, B restored PM integrity by increasing phospholipid (40%), glycolipid (50%) and sulfhydryl group (28%) content, critical for membrane structure and function. It is concluded that B can alleviate root growth inhibition induced by H+ toxicity via increasing the content of key components of PM, which not only repairs the damaged PM but also maintains cellular pH homeostasis through enzyme regulation. The improvement of citrus growth correspondingly safeguards the production capacity.

In modern agricultural practices, agrochemicals and pesticides play an important role in protecting the crops from pests and elevating agricultural productivity. This strategic utilization is essential to meet global food demand due to the relentless growth of the world's population. However, the indiscriminate application of these substances may result in environmental hazards and directly affect the soil microorganisms and crop production. Considering this, an in vitro study was carried out to evaluate the pesticides' effects i.e. lambda cyhalothrin (insecticide) and fosetyl aluminum (fungicide) at lower, recommended, and higher doses on growth behavior, enzymatic profile, total soluble protein production, and lipid peroxidation of bacterial specimens (Pseudomonas aeruginosa and Bacillus subtilis). The experimental findings demonstrated a concentration-dependent decrease in growth of both tested bacteria, when exposed to fosetyl aluminium concentrations exceeding the recommended dose. This decline was statistically significant (p < 0.000). However, lambda cyhalothrin at three times of recommended dose induces 10% increase in growth of Pseudomonas aeruginosa (P. aeruginosa) and 76.8% decrease in growth of Bacillus subtilis (B. subtilis) respectively as compared to control. These results showed the stimulatory effect of lambda cyhalothrin on P. aeruginosa and inhibitory effect on B. subtilis. Pesticides induced notable alterations in biomarker enzymatic assays and other parameters related to oxidative stress among bacterial strains, resulting in increased oxidative stress and membrane permeability. Generally, the maximum toxicity of both (P. aeruginosa and B. subtilis) was shown by fosetyl aluminium, at three times of recommended dose. Fosetyl aluminium induced morphological changes like cellular cracking, reduced viability, aberrant margins and more damage in both bacterial strains as compared to lambda cyhalothrin when observed under scanning electron microscope (SEM). Conclusively the, present study provide an insights into a mechanistic approach of pyrethroid insecticide and phosphonite fungicide induced cellular toxicity towards bacteria.